Endodontic–periodontal Lesions Reconsidered: A Critical Appraisal of Pathogenetic Models, Diagnostic Uncertainty and Treatment Sequencing

Abstract

Endodontic–periodontal lesions occupy a contested position at the intersection of two disciplines that have developed largely separate diagnostic vocabularies, outcome measures and therapeutic traditions. The 2017 World Workshop replaced aetiology-based taxonomies with a scheme organised around the presence of periodontitis and the extent of root damage, a change intended to align classification with prognosis rather than with a causal sequence that is rarely recoverable at the chairside. Whether this reorientation has improved diagnostic reliability or clinical outcomes remains unresolved. This critical narrative review examines the contemporary evidence on endodontic–periodontal lesions, from pathogenetic mechanisms through diagnosis to treatment sequencing and prognosis. The review interrogates four persistent problems: the inferential gap between anatomical communication and demonstrated pathogenetic direction; the weak discriminative performance of the diagnostic tests on which classification depends; the disproportionate influence of a small experimental literature on treatment sequencing recommendations; and the mismatch between the outcome measures used in trials and those that determine tooth retention. Molecular microbiological work has established substantial taxonomic overlap between root canal and periodontal pocket communities, but shared membership is compatible with several directional models and does not by itself establish which compartment seeded the other. Pulp sensibility testing, on which the classification pivots, performs modestly against histological reference standards, and cone-beam computed tomography detects vertical root fracture with sensitivity that falls appreciably in the presence of intracanal radiopaque material. Comparative outcome evidence is dominated by small trials with heterogeneous case definitions; recent syntheses report improvements in probing depth and attachment level across most sequencing strategies without establishing the superiority of any one. Retrospective cohorts report success proportions substantially below those familiar from isolated endodontic or periodontal therapy, with baseline probing depth, apical extent of bone loss and pre-existing periodontitis emerging as consistent prognostic signals. The evidence supports a pragmatic conclusion that root canal treatment should precede definitive periodontal surgical intervention, and a weaker one that the primary determinant of outcome is the extent of attachment loss rather than the treatment sequence chosen. Priorities include prospective cohorts using the current classification with predefined tooth-level endpoints, diagnostic accuracy studies conducted in lesions rather than in surrogate populations, and consensus outcome sets that permit synthesis across the endodontic and periodontal literatures.